U.S. patent application number 10/295373 was filed with the patent office on 2003-10-23 for projection type image display apparatus.
This patent application is currently assigned to Hitachi, Ltd.. Invention is credited to Imahase, Taro, Miyoshi, Tomohiro, Ohishi, Tetsu, Ouchi, Satoshi, Yoshikawa, Hiroki.
Application Number | 20030197944 10/295373 |
Document ID | / |
Family ID | 28672633 |
Filed Date | 2003-10-23 |
United States Patent
Application |
20030197944 |
Kind Code |
A1 |
Ohishi, Tetsu ; et
al. |
October 23, 2003 |
Projection type image display apparatus
Abstract
A projection type image display apparatus includes a light axis
moving unit for moving a direction of a light from a light source
substantially in parallel periodically at a predetermined rate, a
light separating unit for separating the light from the light axis
moving unit into a plurality of color light components of
predetermined wavelength bands, and a radiation unit for radiating
the color light components from the light separating unit on an
image display device, projecting an optical image corresponding to
the image signal in enlarge form.
Inventors: |
Ohishi, Tetsu; (Hiratsuka,
JP) ; Yoshikawa, Hiroki; (Hiratsuka, JP) ;
Ouchi, Satoshi; (Kamakura, JP) ; Imahase, Taro;
(Fujisawa, JP) ; Miyoshi, Tomohiro; (Fujisawa,
JP) |
Correspondence
Address: |
TOWNSEND AND TOWNSEND AND CREW, LLP
TWO EMBARCADERO CENTER
EIGHTH FLOOR
SAN FRANCISCO
CA
94111-3834
US
|
Assignee: |
Hitachi, Ltd.
Tokyo
JP
|
Family ID: |
28672633 |
Appl. No.: |
10/295373 |
Filed: |
November 14, 2002 |
Current U.S.
Class: |
359/634 ;
348/E5.141; 348/E9.027 |
Current CPC
Class: |
G02B 26/00 20130101;
G02B 27/1053 20130101; H04N 9/3117 20130101; H04N 5/7441 20130101;
G02B 27/1033 20130101; G02B 27/148 20130101 |
Class at
Publication: |
359/634 |
International
Class: |
G02B 027/14 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 17, 2002 |
JP |
2002-114113 |
Claims
What is claimed is:
1. An image display apparatus for separating the light from a light
source into a plurality of color light components of predetermined
wavelength bands and radiating the separated light components
periodically on an image display device to project an optical image
corresponding to the image signal in an enlarged form, comprising:
light moving unit which moves the direction of the light from said
light source substantially in parallel periodically at a
predetermined rate; light separating unit which separates said
light from said light moving unit into a plurality of color light
components of predetermined wavelength bands; and radiation unit
which radiates the color light components from said light
separating unit on said image display device; wherein an optical
image corresponding to the image signal is projected in enlarged
form.
2. An image display apparatus for separating the light from a light
source into a plurality of color light components of predetermined
wavelength bands and radiating the separated light components
periodically on an image display device to project an optical image
corresponding to the image signal in an enlarged form, comprising:
light moving unit which moves the direction of the light from said
light source substantially in parallel periodically at a
predetermined rate; light separating unit which separates said
light from said light moving unit into a plurality of color light
components of predetermined wavelength bands; radiation unit which
radiates a plurality of said color light components from said light
separating unit selectively on a single reflection type image
display device; and emitting unit which emits the color light
components modulated and reflected by said image display device, in
a direction different from said light separating unit; wherein an
optical image corresponding to the image signal emitted from said
emitting unit is projected in enlarged form.
3. An image display apparatus for separating the light from a light
source into a plurality of color light components of predetermined
wavelength bands and radiating the separated light components
periodically on an image display device to project an optical image
corresponding to the image signal in an enlarged form, comprising:
light moving unit which moves the direction of the light from said
light source substantially in parallel periodically at a
predetermined rate; light separating unit which separates said
light from said light moving unit into a plurality of color light
components of predetermined wavelength bands; and radiation unit
which bends a plurality of said color light components from said
light separating unit in a predetermined direction and selectively
radiating said bent color light components on a single reflection
type image display device; and wherein an optical image
corresponding to the image signal reflected from said reflection
type image display device is projected in enlarged form.
4. An image display apparatus according to claim 1, wherein said
light separating unit includes a plurality of reflection films
arranged diagonally with respect to the optical axis for
selectively reflecting the color components to be separated, said
reflection films being arranged in a predetermined spaced relation
with each other in the order of the colors to be separated.
5. An image display apparatus according to claim 2, wherein said
light separating unit includes a plurality of reflection films
arranged diagonally with respect to the optical axis for
selectively reflecting the color components to be separated, said
reflection films being arranged in a predetermined spaced relation
with each other in the order of the colors to be separated.
6. An image display apparatus according to claim 3, wherein said
light separating unit includes a plurality of reflection films
arranged diagonally with respect to the optical axis for
selectively reflecting the color components to be separated, said
reflection films being arranged in a predetermined spaced relation
with each other in the order of the colors to be separated.
7. An image display apparatus according to claim 4, wherein the
number of layers of said reflection films is equal to twice the
number of the color components to be separated, less one.
8. An image display apparatus according to claim 4, wherein said
light separating unit includes, on at least on one side thereof, a
plurality of transparent flat plates with a trapezoidal section
each having a reflection film for selectively reflecting the colors
to be separated.
9. An image display apparatus according to claim 5, wherein said
light separating unit includes, on at least on one side thereof, a
plurality of transparent flat plates with a trapezoidal section
each having a reflection film for selectively reflecting the colors
to be separated.
10. An image display apparatus according to claim 6, wherein said
light separating unit includes, on at least on one side thereof, a
plurality of transparent flat plates with a trapezoidal section
each having a reflection film for selectively reflecting the colors
to be separated.
11. An image display apparatus according to claim 4, wherein said
reflection films of said light separating unit are arranged between
one of the rectangular surfaces of a prism and one of the
rectangular surfaces of a trapezoid prism and also between the
opposed rectangular surfaces of a plurality of trapezoid
prisms.
12. An image display apparatus according to claim 5, wherein said
reflection films of said light separating unit are arranged between
one of the rectangular surfaces of a prism and one of the
rectangular surfaces of a trapezoid prism and also between the
opposed rectangular surfaces of a plurality of trapezoid
prisms.
13. An image display apparatus according to claim 6, wherein said
reflection films of said light separating unit are arranged between
one of the rectangular surfaces of a prism and one of the
rectangular surfaces of a trapezoid prism and also between the
opposed rectangular surfaces of a plurality of trapezoid
prisms.
14. An image display apparatus according to claim 8, wherein a
transparent member is arranged on at least one surface of said
light separating unit.
15. An image display apparatus according to claim 9, wherein a
transparent member is arranged on at least one surface of said
light separating unit.
16. An image display apparatus according to claim 10, wherein a
transparent member is arranged on at least one surface of said
light separating unit.
17. An image display apparatus according to claim 8, wherein two of
said reflection films of said light separating unit for reflecting
the same color light component have an upper layer thereof smaller
in reflectivity than a lower layer thereof.
18. An image display apparatus according to claim 8, wherein the
media between said reflection films of said light separating unit
include a medium on the reflection surface of said reflection film
of said upper layer having a refractive index smaller than a medium
on the reflection surface of said reflection film of said lower
layer.
19. An image display apparatus according to claim 11, wherein a
transparent member is arranged on at least on one side of said
light separating unit.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to an image display apparatus
such as a liquid crystal projection apparatus, a reflection type
image display projection apparatus or a projection type display
apparatus for projecting an image on the screen using an image
display device such as a transmission type liquid crystal panel or
a reflection type image display device as a light bulb, or in
particular to a technique whereby the light from a light source is
separated into color light components of predetermined wavelength
bands and radiated periodically on an image display device. In this
way, the light from the light source of an image display apparatus
for projecting an optical image corresponding to an image signal in
enlarged form is separated into color light components of
predetermined wavelength bands and radiated on the image display
device.
[0002] In the image display apparatus, an image display device is
required for each color because a color image is obtained by
projecting the image for each of the colors including red, green
and blue, for example, having predetermined wavelengths at a single
point. In view of the fact that the image display device is
expensive on the one hand and the need of saving energy on the
other hand, however, a method has been employed in which images of
a plurality of colors are displayed with a single image display
device.
[0003] The conventional image display apparatus comprising a single
image display device will be explained with reference to FIG.
7.
[0004] FIG. 7 is a schematic diagram for explaining the
configuration of the essential parts of the conventional image
display apparatus. In the image display apparatus shown in FIG. 7,
the light emitted from a light source 2 of a lamp such as a
high-pressure mercury lamp included in a light source unit 1 is
reflected from a condensing reflector 3 and enters a cross prism 22
for color separation. The cross prism 22 includes reflection films
crossed so as to reflect two types of light, and separates the
light into the three color light components of red, green and blue
by reflection and transmission.
[0005] Each color light component thus separated enters into
optical axis moving units 4B, 4G, 4R for moving the optical axis in
substantially parallel directions, and makes up the light
components 24, 25, 26 with the optical axes thereof repeatedly
moved in substantially parallel directions. The optical axis moving
units are implemented by moving reflectors in parallel or by
rotating a parallelepiped and causing the light to enter into it in
the direction perpendicular to the rotational axis thereby to
displace the optical axis horizontally with parallel flat
plates.
[0006] The light components 24, 25, 26 with the optical axes
thereof repeatedly moved substantially in parallel enter the
reflectors 23B, 23G, 23R arranged in obliquely spaced relation with
each other for reflecting each color component selectively. The
light components of the three colors are sequentially synthesized
and radiated on the image display device. In the process, the
positions of the three color light components are controlled
individually by the optical axis moving units in order to prevent
the color light components from radiating the same position of the
image display device 6 at the same time and to prevent the color
components from being mixed with each other.
[0007] Each light component thus radiated is modulated by the image
of the particular color, and the modulated image light component of
each color is projected in enlarged form on a screen 8 through a
projection lens 7 thereby to produce a color image.
SUMMARY OF THE INVENTION
[0008] The conventional image display apparatus having the
configuration described above poses the problem that in spite of
the need of a single image display device, the optical axis moving
unit is required for each color. Therefore, the apparatus is bulky,
and it is difficult to obtain a compact and inexpensive
apparatus.
[0009] The object of this invention is to provide a compact image
display apparatus by obviating this problem.
[0010] In order to achieve the object described above, according to
this invention, there is provided an image display apparatus for
separating the light from a light source into color light
components of predetermined wavelength bands and radiating them
periodically on an image display device thereby to project an
optical image corresponding to an image signal in enlarged form,
the apparatus comprising an optical axis moving unit for moving the
direction of the light from the light source periodically at a
predetermined rate substantially in parallel and a light separating
unit for separating the light from the optical axis moving unit
into color light components of a plurality of predetermined
wavelength bands, wherein the color light components emitted from
the light separating unit are radiated on the image display device
thereby to project an optical image corresponding to the image
signal in enlarged form.
[0011] In the image display apparatus according to this invention,
the direction of the light proceeding from the light source is
moved periodically in parallel by the optical axis moving unit,
after which the light is separated into a plurality of color light
components having predetermined wavelength bands and radiated on
the image display device. As a result, a fewer number of optical
axis moving units are used, thereby making it possible to produce a
compact image display apparatus.
[0012] Other objects, features and advantages of the invention will
become apparent from the following description of the embodiments
of the invention taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a diagram showing an optical configuration of an
image display apparatus according to a first embodiment of this
invention.
[0014] FIGS. 2A to 2F are schematic diagrams for explaining the
principle of the image display apparatus and diagrams for
explaining the distribution of the light radiated on the image
display device according to the invention.
[0015] FIG. 3 is a diagram showing an optical configuration of an
image display apparatus according to a second embodiment of this
invention.
[0016] FIG. 4 is a diagram showing an optical configuration of an
image display apparatus according to a third embodiment of this
invention.
[0017] FIG. 5 is a schematic diagram for explaining a light
separating unit used with the image display apparatus according to
the invention.
[0018] FIG. 6 is a schematic diagram for explaining another light
separating unit used with the image display apparatus according to
the invention.
[0019] FIG. 7 is a diagram showing an optical configuration for
explaining the conventional image display apparatus.
DESCRIPTION OF THE EMBODIMENTS
[0020] Several embodiments of the invention will be explained below
with reference to the accompanying drawings.
[0021] FIG. 1 is a diagram showing an optical configuration
according to a first embodiment of the invention, and illustrates
an image display apparatus using a single transmission type image
display device as a light bulb.
[0022] In FIG. 1, reference numeral 1 designates a light source
unit, numeral 2 a light source, numeral 3 a reflector, numeral 4 an
optical axis moving unit for moving the position of the optical
axis of the light radiated, numeral 5 a light separating unit for
separating the light into light fluxes having a plurality of
predetermined wavelength bands of such as red, green and blue color
components, numeral 6 a display device for modulating and
displaying the light, numeral 7 a projection unit for projecting,
in enlarged form, the image light modulated by the display device,
and numeral 8 a screen.
[0023] The image display apparatus comprises the light source unit
1 having the light source 2, which is a white lamp such as an
ultrahigh pressure mercury lamp, a metal halide lamp, a xenon lamp,
a mercury xenon lamp or a halogen lamp.
[0024] The light emitted from the light source 2 is condensed and
reflected by the reflector 3 having an elliptic, parabolic or
aspheric surface.
[0025] The illuminance distribution is improved and the radiation
range defined by a pair of condensing lenses or collimator lenses
(not shown) arranged in a rectangular frame substantially of the
same size as the exit opening of the reflector 2. The resulting
light is converted by polarization through a polarization
conversion device (not shown) as required and emitted from the
illumination unit.
[0026] The light 9 emitted from the illumination unit 1 enters into
the optical axis moving unit 4. The optical axis moving unit 4
moves the optical axis repeatedly substantially in parallel by such
a method as moving the light reflectors in parallel or rotating a
parallelepiped and causing the light to enter into in the direction
perpendicular to the rotational axis thereby to displace the
optical axis horizontally with parallel flat plates.
[0027] The light 10 that has left the optical axis moving unit 4
enters into the light separating unit 5. The light separating unit
5 includes a first light reflector 5R1 for reflecting the light
component of the red wavelength band and transmitting the light
components of the other wavelength bands, a second light reflector
5B1 for reflecting the light of the blue wavelength band and
transmitting the light of the other wavelength bands, a third light
reflector 5G for reflecting the light of the green wavelength band
and transmitting the light of the other wavelength bands, a fourth
light reflector 5R2 for reflecting the light of the red wavelength
band and transmitting the light of the other wavelength bands and a
fifth light reflector 5B2 for reflecting the light of the blue
wavelength band and transmitting the light of the other wavelength
bands. All of these light reflectors are tilted with respect to the
optical axis and arranged in spaced relation with each other to
avoid the mixing between adjacent colors. The light 10 that has
left the optical axis moving unit 4, therefore, first has the blue
component thereof reflected by the second light reflector 5B1, and
after being transmitted through the first light reflector 5R1,
radiates the blue light component 11B on one edge of the image
display device at the position shown. The red and green light
components transmitted through the second light reflector 5B1, on
the other hand, have the green light component thereof reflected by
the third light reflector 5G and after being transmitted through
the second light reflector 5B1, radiate the green light component
11G at substantially the center of the image display device
through. Also, the red light component transmitted through the
third light reflector 5G has the red light component thereof
reflected by the fourth light reflector 5R2 and after being
transmitted through the third light reflector 5G, radiates the red
light component 11R at the image display device at an edge
different from the position irradiated with the blue light
component 11B. The light 10, that has left the optical axis moving
unit 4 is emitted while moving to a different position from FIG. 1,
is radiated on the image display device by being separated into
color components corresponding to the incident position of the
light separating unit 5. Therefore, the movement of the light by
the optical axis moving unit 4 also moves the color components
radiated on the image display device.
[0028] The light radiated on the image display device 6 is
modulated by the image on the display surface of the display device
6 and exits from it. This exit light is enlarged by the projection
lens 7 or the like and projected in enlarged form on the screen 8
thereby to produce a color image.
[0029] Now, the operation in which the color light components
radiated on the image display device 6 by the light separating unit
5 are moved with the movement of the light by the optical axis
moving unit 4 will be explained in detail with reference to FIGS.
2A to 2F.
[0030] FIGS. 2A to 2F are schematic diagrams for explaining the
principle in which with the movement of the light by the optical
axis moving unit 4 of the image display apparatus according to the
invention, the light is separated into predetermined color light
components by the light separating unit 5 on the one hand, and
diagrams for explaining the distribution of the light radiated on
the image display device on the other hand.
[0031] In FIGS. 2A to 2F, the light 10 leaving the optical axis
moving unit 4 moves in parallel to the direction of dashed arrow
with the light fluxes of width w from the light source. Assume that
the light indicated at the position shown in FIG. 2A is the light
10a, the light indicated at the position shown in FIG. 2B is the
light 10b, the light indicated at the position shown in FIG. 2C is
the light 10c, the light indicated at the position shown in FIG. 2D
is the light 10d, the light indicated at the position shown in FIG.
2E is the light 10e and the light indicated at the position shown
in FIG. 2F is the light 10f. The light 10 at each position is
radiated on the image display device while moving in colored form
as shown by being separated through the five light reflectors of
the light separating unit 5. The light 10 leaving the optical axis
moving unit 4, therefore, upon movement in parallel to the
direction of dashed arrow with the light fluxes of width w from the
light source, is moved and radiated with each color separated. As
described above, each color separated in similar fashion is moved
also on the screen. Once the parallel movement goes through a
cycle, every position is displayed with all the colors. In the case
where the repetitive period is not less than about 60 cycles per
second, therefore, viewers can observe a color image.
[0032] The width w of the light flux is set to such a value that
the light is radiated in a range narrower than one third of the
width of one side on the image display device, taking the avoidance
of color mixing, the light utilization factor and the size of the
non-image display section into consideration. For this purpose, an
optical device such as a lens may be provided in the light path to
define the radiation range and improve the illuminance of the light
9 leaving the illumination unit as required.
[0033] According to the embodiments of the invention, the light to
be separated into the color light components of the wavelength
bands of red, blue and green is selectively reflected by five
reflection films (light reflectors) arranged diagonally with
respect to the optical axis and in spaced relation with each other
in the order of separation of the respective color light
components. Nevertheless, the reflection films may be in the number
twice the number of the color light components into which the light
is to be separated, less one. In the case where the light is
separated into two color light components, for example, three
reflection films are arranged diagonally with respect to the
optical axis.
[0034] In the image display apparatus according to the invention
described above, the direction in which the light proceeds from the
light source is moved periodically, and the light, after being
separated into a plurality of color light components of
predetermined wavelength bands and emitted, is radiated on the
image display device thereby to project an optical image
corresponding to the image signal in enlarged form. As a result, an
inexpensive, compact image display apparatus can be configured with
a single image display device and a single optical axis moving
unit.
[0035] The embodiment described above employs a transmission type
image display device as a light bulb. Now, an explanation will be
given of a second embodiment employing a reflection type image
display device, or especially, a single image display device
utilizing the polarization.
[0036] FIG. 3 is a diagram showing an optical configuration of an
image display apparatus according to a second embodiment of the
invention, in which a single reflection type image display device
utilizing the polarization is used as a light bulb.
[0037] In FIG. 3, numeral 12 designates a polarizing reflector for
transmitting or reflecting the light by polarization. Numerals 4 to
11 designate the same component parts as those designated by the
same reference numerals, respectively, in the first embodiment.
[0038] In this image display apparatus, like in the first
embodiment, the light from a light source enters into the optical
axis moving unit 4 through a group of optical devices (not shown)
for improving the illuminance distribution, defining the range of
radiation and conversion by polarization. The optical axis moving
unit 4 is adapted to move the optical axis repeatedly substantially
in parallel by a method in which the light reflectors are moved in
parallel or a method in which a parallelepiped is rotated and the
light is caused to enter into in the direction perpendicular to the
rotational axis thereby to shift the optical axis horizontally by
use of a parallel flat plate.
[0039] The light 10 that has left the optical axis moving unit 4
enters into the light separating unit 5. The light that has entered
into the light separating unit 5 exits after being separated into
the three light components including the red light component 11R,
the green light component 11G and the blue light component 11B by
the light reflectors for selectively reflecting the light
components in each wavelength band in the same manner as in the
first embodiment.
[0040] The light that has exited from the light separating unit 5
enters into the polarizing reflector 12 arranged diagonally. In the
case where the polarized light transmitted through the polarizing
light reflector 12 is combined with the polarized light leaving the
light separating unit 5, the light that has exited from the light
separating unit 5 is transmitted through the polarizing reflector
12 and radiated on the image display device 6. As in the first
embodiment, assume that the light 10 that has exited from the
optical axis moving unit 4 exits by moving to a position different
from the position indicated in FIGS. 2E, 2F. Then, the light is
separated into the color components corresponding to the point of
incidence of the light separating unit 5 described above and
radiated on the image display device. Once the light is moved by
the optical axis moving unit 4, therefore, the color light
components radiated on the image display device are also moved.
[0041] The light radiated on the image display device 6 is changed
in polarization by being modulated with the image on the display
surface. The light that has entered into the image display device
as the S polarized light, for example, is modulated into the P
polarized light. As a result, the light modulated and leaving the
image display device 6 is reflected on the polarizing reflector 12,
and projected on the screen 8 in enlarged form through the
projection lens 7 or the like thereby to produce an enlarged color
image.
[0042] In the image display apparatus according to the invention,
the light is moved by the optical axis moving unit 4 while being
separated into predetermined color light components on the same
principle as in the first embodiment.
[0043] As described above, with the image display apparatus
according to this invention, the direction in which the light from
the light source proceeds is moved periodically at a predetermined
rate substantially in parallel, and the exit light is separated
into a plurality of color light components of predetermined
wavelength bands. The predetermined polarized exit light components
thus separated are selectively radiated on a single reflection type
display device. At the same time, the polarized light modulated by
the image display device is emitted in a direction different from
the direction of incidence of the separated light, so that an
optical image corresponding to the exit image signal is projected
in enlarged form. Thus, an inexpensive, compact image display
apparatus can be configured of a single reflection type image
display device and a single optical axis moving unit.
[0044] The embodiment described above represents a case in which a
reflection type image display device utilizing the polarization is
employed as a light bulb. An explanation will be given below of a
third embodiment employing a single reflection type image display
device having a plurality of fine light reflectors.
[0045] FIG. 4 is a diagram showing an optical configuration of an
image display apparatus according to a third embodiment of the
invention, which employs a single reflection type image display
device having a plurality of fine light reflectors as a light
bulb.
[0046] In FIG. 4, numeral 13 designates a hologram device having
the function of bending the light in a predetermined direction.
Numerals 4 to 11 designate the same component parts as the
corresponding numerals, respectively, in the first embodiment.
[0047] In the image display apparatus according to this embodiment,
like in the first embodiment, the light of a light source enters
into the optical axis moving unit 4 through a group of optical
devices (not shown) for improving the illuminance distribution and
defining the radiation range of the light from the light source.
The optical axis moving unit 4 repeatedly moves the optical axis
substantially in parallel repeatedly by moving the light reflectors
in parallel or by rotating a parallelepiped thereby to cause the
light to enter it in the direction perpendicular to the rotational
axis and thereby displacing the optical axis horizontally using a
parallel flat plate.
[0048] The light 10 that has left the optical axis moving unit 4
enters into the light separating unit 5. The light that has entered
into the light separating unit 5, like in the first embodiment,
exits by being separated into the three color light components
including the red light component 11R, the green light component
11G and the blue light component 11B through the light reflectors
for selectively reflecting the light of each wavelength band.
[0049] The light that has left the light separating unit 5 enters
into the hologram device 13, and exiting it with the optical axis
thereof bent to a predetermined angle, is radiated on the image
display device 6. As in the first embodiment, the light 10, which
leaves the optical axis moving unit 4 while moving to a position
different from that in FIGS. 2E, 2F, is radiated on the image
display device by being separated into a plurality of color
components corresponding to the incident point of the light
separating unit 5. With the movement of the light by the optical
axis moving unit 4, therefore, the color light components radiated
on the image display device 6 are also moved.
[0050] The image display device 6 having a plurality of fine light
reflectors functions to change the angle of the fine reflection
surface in accordance with the image and thereby lead the
image-displaying light in the direction perpendicular to the image
display device 6 while leading the non-image-displaying light to
such an angle as to be prevented from entering into the projection
lens. As a result, the color light components radiated on the image
display device 6 are reflected in accordance with the image
associated with a particular color component and projected in
enlarged form on the screen by the projection lens 7 or the like
thereby to produce a color image.
[0051] In the image display apparatus according to this invention,
the movement of the light by the optical axis moving unit 4 causes
the light separating unit 5 to move the light by separating it into
predetermined color light components on the same principle as in
the first embodiment.
[0052] In the image display apparatus according to this invention
described above, the direction in which the light from the light
source proceeds is periodically changed and the exit light is
separated into a plurality of color light components of
predetermined wavelength bands. The exit light components thus
separated are bent in a predetermined direction and radiated on a
single reflection type image display device, so that an optical
image corresponding to the image signal emitted from the particular
image display device is projected in enlarged form. Therefore, an
inexpensive, compact image display apparatus of reflection type is
provided by a single reflection type image display device having a
plurality of fine light reflectors and a single optical axis moving
unit.
[0053] According to the embodiment described above, reflection
films for selectively reflecting the color light components
separated by the light separating unit are arranged diagonally with
respect to the optical axis in spaced relation with each other in
the order of the colors separated. Various methods can be employed
to attain this purpose, and some of them will be explained
below.
[0054] FIG. 5 is a diagram for explaining a light separating unit
of the image display apparatus according to another embodiment of
the invention.
[0055] In FIG. 5, the light separating unit 5 entered by the light
10 is configured of a prism 14 formed with a first light reflector
5R1 for reflecting the light component in red wavelength band on
one of the rectangular surfaces of the prism having a triangular
section and transmitting the color light components having the
other wavelength bands, a trapezoid prism 15 formed with a second
light reflector 5B1 for reflecting the light component in blue
wavelength band on one of the rectangular surfaces of the trapezoid
prism having a trapezoidal section and transmitting the color light
components having the other wavelength bands, a trapezoid prism 16
formed with a third light reflector 5G for reflecting the light
component in green wavelength band on one of the rectangular
surfaces of the trapezoid prism having a trapezoidal section and
transmitting the color light components having the other wavelength
bands, a trapezoid prism 17 formed with a fourth light reflector
5R2 for reflecting the light component in red wavelength band on
one of the rectangular surfaces of the trapezoid prism having a
trapezoidal section and transmitting the color light components
having the other wavelength bands and a trapezoid prism 18 formed
with a fifth light reflector 5B2 for reflecting the light component
in blue wavelength band on one of the rectangular surfaces of the
trapezoid prism having a trapezoidal section and transmitting the
color light components having the other wavelength bands. All of
these light reflectors are stacked with the first to fourth
reflection films tilted with respect to the optical axis and
arranged in spaced relation with each other to avoid the adjacent
colors from mixing with each other. The light 10 that has left the
optical axis moving unit 4, therefore, first has the blue component
reflected on the second light reflector 5B1 at the position shown
in FIG. 5, and after being transmitted through the first light
reflector 5R1, radiates the blue light component 11b on one of the
edges of the image display device. The red and green light
components transmitted through the second light reflector 5B1, on
the other hand, have the green component reflected on the third
light reflector 5G, and after being transmitted through the second
light reflector 5B1, radiates the green light component 11G
substantially at the center of the image display device. Also, the
red light component that has been transmitted through the third
light reflector 5G is reflected on the fourth light reflector 5R2,
and after being transmitted through the third light reflector 5G,
radiated as a red light component 11R on an edge of the image
display device different from the point irradiated with the blue
light component 11B. When the light 10 that has left the optical
axis moving unit (not shown) exits by moving to a different
position from that shown in FIG. 6, it is separated into color
light components corresponding to the point of incidence to the
light separating unit 5 described above and then radiated on the
image display device. With the movement of the light by the optical
axis moving unit 4, therefore, the color light components radiated
on the image display device are also moved, thereby producing the
same effects as those described in the first embodiment.
[0056] The apparatus according to the invention does not
necessarily employ the aforementioned configuration in which the
reflection films for separating the light into a plurality of color
light components of predetermined wavelength bands are interposed
between one of the rectangular surfaces of the prism and one of the
rectangular surfaces of the trapezoid prism on the one hand and
between the opposed rectangular surfaces of a plurality of the
trapezoid prisms on the other hand. Alternatively, a plurality of
units for separating the light into a plurality of color light
components of predetermined wavelength bands are so configured that
a plurality of transparent flat plates each having a trapezoidal
section formed, on at least one side thereof, with a reflection
film for selectively reflecting the colors to be separated are
stacked in predetermined spaced relation with each other, thereby
making it possible to produce a similar effect.
[0057] The embodiments described above have been described based on
the main light components. Actually, however, the light emitting
portion of the light source has a finite length, and therefore the
light has an expansion. An embodiment with a large expansion of the
light will be explained below.
[0058] FIG. 6 is a diagram for explaining the light separating unit
of an image display apparatus according to another embodiment of
the invention.
[0059] In FIG. 6, the light separating unit 5 has the same
configuration as the light separating unit 22 described above,
except that the light separating unit 5 is defined by transparent
members 19, 20, 21 on the three sides thereof. The functions of the
reflection surface are identical to those of the embodiment
described above, and therefore will not be explained. In the light
separating unit 5 having this configuration, the incident light 10a
having a large expansion is transmitted through a transparent
member 20, and after being reflected on a second reflection surface
through a trapezoid prism 15, leaves the light separating unit 5
through the trapezoid prism 15 and the transparent member 19. The
incident light enters the trapezoid prism at a large incidence
angle, or generally about 80 degrees. In the absence of the
transparent member 19, therefore, the light is reflected on the
incidence surface. According to this embodiment, this reflection is
not caused in the presence of the transparent member 19 and
therefore the light utilization factor is high.
[0060] In the case where the incidence point is different, the
incident light 10b having a large expansion is transmitted through
the transparent member 20 and reflected on the fourth reflector 5R2
through the trapezoid prism 15 formed with the second light
reflector 5B1, the trapezoid prism 16 formed with the third light
reflector 5G and the trapezoid prism 17 formed with the fourth
light reflector 5R2. Then the light is reflected from the fourth
reflector 5R2 and exits from the light separating unit 5 through
the trapezoid prism 17 and the transparent member 21. In this case,
the incident light enters into the transparent member 1 from the
trapezoid prism 17 at a large incidence angle, or generally, at
about 80 degrees. In the absence of the transparent member 21,
therefore, the light would be reflected on the incident surface.
According to this embodiment, however, the presence of the
transparent member 21 prevents such reflection and therefore a high
light utilization factor is achieved, while at the same time
avoiding the color mixing which otherwise might be caused by
irregular reflection.
[0061] Also in the case where the incident point is different, the
incident light 10c having a large expansion is transmitted through
the transparent member 20 and reflected on the third reflector 5G
through the trapezoid prism 16 formed with the third light
reflector 5G. The light thus reflected exits from the light
separating unit 5 through the trapezoid prisms 15, 16 and the
transparent member 20. In this case, the incident light enters into
the transparent member 20 from the trapezoid prism 16 at a large
angle, or generally, at about 80 degrees. In the absence of the
transparent member 20, therefore, the light would be reflected on
the incident surface. According to this embodiment, however, the
presence of the transparent member 20 prevents such reflection, and
therefore a high light utilization factor is achieved, while at the
same time avoiding the color mixing which otherwise might be caused
by irregular reflection.
[0062] These effects depend on the expansion angle of the light.
Therefore, the transparent member is not necessarily included in
the light separating unit 3 and only a practically effective
surface thereof may have a transparent member.
[0063] The transparent member is preferably configured of a
material having substantially the same refractive index as the
trapezoid prism not to cause any refraction of the light on the
bonding surface.
[0064] Also, the light separating unit according to this invention
has a different number of reflection films and hence a different
light amount passed through a light path depending on the light
incidence point. This causes the irregularities of the brightness
or color of the image. Therefore, the light separating unit can be
configured alternately as described below. For example, the
reflection films for separating the light into a plurality of the
color light components of predetermined wavelength bands include an
upper reflection film and a lower reflection film, the former
having a smaller reflectivity than the latter. As a result, the
difference of the transmittance between the light paths reflected
by the upper and lower reflection films can be reduced thereby to
realize a more uniform image. Also, a unit for absorbing a
predetermined light is arranged on at least one of the incident
surface and the exit surface of the unit for separating the light
into a plurality of the color light components of predetermined
wavelength bands, and the magnitude of absorption is so adjusted as
to reduce the difference of the light amount between the path
formed by the light reflected from the upper layer and the path
formed by the light reflected from the lower layer thereby to
realize a more uniform image.
[0065] The light separating unit according to this invention can
differentiate the light path and the light path length depending on
the incident point of the light. This might differentiate the
distribution of the light radiated on the image display device and
cause the irregularities of the brightness or color of the image.
To obviate this, the following alternative configuration can be
employed.
[0066] The media between the reflection films for separating the
light into a plurality of color light components of predetermined
wavelength bands are so configured that the refractive index of the
medium on the reflection surface of the uppermost reflection film
layer is smaller than the refractive index of the medium on the
reflection surface side of the lowest reflection film layer. This
configuration can reduce the difference of the light path length
between the uppermost and the lowest layers converted in terms of
the same refractive index into which the light path length is
converted. As a result, the difference of the distribution of the
light radiated on the image display device can be reduced thereby
to reduce the irregularities of the brightness and the color of the
image.
[0067] In spite of the foregoing explanation about the lowest
reflection film layer limited to a selective color, the reflection
is not necessarily limited to a selective color in view of the fact
that the light entering the reflection film is the remainder after
reflection of two color light components. This makes it possible to
use a light reflector of a higher reflectivity, thereby improving
the brightness.
[0068] Also, the spectral characteristic of each reflection film of
the light separating unit is such as to eliminate the yellow and
orange color components requiring no image color adjustment and
thus to allow the unrequired light components to pass through the
light separating unit. The light components that have been
transmitted through each reflection film of the light separating
unit are absorbed to prevent the stray light from being scattered
in the image display apparatus. As a result, the deterioration of
the contrast which otherwise might be caused by the scattered light
can be prevented.
[0069] According to the embodiments of the invention described
above, the red, green and blue color reflection films of the light
separating unit are arranged in that order. Nevertheless, the
reflection films may be arranged in a different order of colors,
and is not limited to these color components. The effects of the
image display apparatus according to the invention thus can be
produced by a configuration in which the direction of the light
proceeding from the light source is moved periodically, the exit
light is separated into a plurality of color light components of
predetermined wavelength bands, the exit light components separated
are radiated on the image display device and an optical image
corresponding to the image signal is projected in enlarged
form.
[0070] Further, the embodiments of the invention are described
above, in which the direction of the light proceeding from the
light source is set in vertical direction. The invention is not
limited to this direction, but is also apparently applicable to the
movement of light in horizontal direction.
[0071] Furthermore, the foregoing description of the embodiments of
the invention handles a unit by which the light leaving the light
separating unit is radiated directly on the image display device.
Nevertheless, the illumination light may be condensed at the focal
point in or in the neighborhood of the light separating unit, the
object surfaces of the relay lens having substantially the same
magnification are rendered substantially coincident with the focal
point, and the image surface position of the relay lenses is
rendered substantially coincident with the position of the image
display device, thereby making it possible to radiate the
illumination light on the image display device accurately. Thus,
the color mixing can be avoided with a high efficiency.
[0072] In the image display apparatus according to this invention,
the light is passed through the optical axis moving unit in which
the direction of the light proceeding from the light source is
periodically moved, and then the light is separated into a
plurality of color light components of predetermined wavelength
bands before being radiated on the image display device. Therefore,
a fewer optical axis moving units can be employed than in the prior
art, thereby realizing a compact image display apparatus.
[0073] It should be further understood by those skilled in the art
that although the foregoing description has been made on
embodiments of the invention, the invention is not limited thereto
and various changes and modifications may be made without departing
from the spirit of the invention and the scope of the appended
claims.
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